1. Field of the Invention
The present invention relates to an electrostatic charge image developing toner.
2. Description of the Related Art
Nowadays, electrostatic latent image development method is widely adapted to image formation process using printer, copying machine, facsimile and so forth.
This is because the method has a high degree of completion which can ensure rapid and stable formation of high-quality image. Several problems, however, still remain unsolved.
For example, it is difficult for an earlier developed toners prepared by the grinding process to keep an inter-particle uniformity in the surface property due to non-uniform distribution of materials dispersed in the toner on the fractured surface, and this tends to cause non-uniformity in the transfer process, and to thereby degrade the color reproducibility in color images.
On the other hand, another demand for the electrostatic latent image toner is to reduce the particle size in view of upgrading the image quality. Extensive efforts for producing small-particle-size toner have recently been directed to development of “chemical toner”, of which particle is formed in a water-base medium. Methods of preparing the chemical toner include those such as preparing irregular-shaped toner particle by allowing resin particle and optional colorant to proceed association, salting-out, coagulation or fusing; and such as dispersing a radical polymerizable monomer and colorant and then allowing the mixture to proceed droplet dispersion in a water-base medium so as to obtain a desired particle size, and allowing the dispersion to proceed emulsion polymerization.
The toner particle obtained by the emulsion polymerization process is advantageous in raising inter-particle uniformity in shape because the process is successful in forming the toner particle having a spherical shape and a uniform surface property, but the particle distribution size is wide, resulting in raising a problem of degrading the cleaning property or causing a toner dispersion.
As one measure for addressing this problem, a spherical particle produced by treating a resin particle, prepared in a water-base medium containing a surfactant, with a coagulant in an amount larger than the critical coagulation concentration of the resin particle and an organic solvent freely miscible with water (see e.g., JP-Tokukaihei-11-194540A).
An emulsion-polymerized toner (see e.g., JP-1744009B) and fusion emulsification process (see e.g., JP-Tokukaihei-9-15902A), which are based on a technique of mechanically dispersing a monomer oil droplet or resin solution droplet under the presence of an inorganic dispersant, can only attain a particle size of as small as 7 μm, and are therefore not suitable for obtaining a sharp particle size distribution in principle. Use of a surfactant is indispensable for forwarding size reduction of the toner particle. Although most portion of an unnecessary residue of the surfactant in this case can be removed when the particle is separated from the water-base medium, problems may arise in that the surfactant still remaining in the particle inhibits electrostatic charging of the toner depending on types and residual amount of the surfactant, or in that the surfactant reacts with a metal ion contained in a pigment so as to form an insoluble salt, and the resultant salt is causative of contamination of a friction electrostatic charging member or a photosensitive material, or inhibition of the toner particle per se.